1. Field of the Invention
The present invention relates to a pipe-like component for connecting pipes to other assemblies, for example for connecting fuel lines to other components of the fuel supply system, such as the tank.
2. Discussion of the Background
In the context of the ever-stricter demands for reducing hydrocarbon emissions from vehicles, improving the performance of connectors is becoming increasingly important. The connection of fuel lines to a plastic fuel tank, for example, proves especially problematic, since the incompatibility of the different materials means that the lines must be connected by means of welded-on polyethylene (PE) nipples. This material, however, has a high creep tendency, so that conventionally constructed connections between pipe and nipple, for example using quick-action couplings, fail because within a short period of time they begin to leak due to creeping of the PE.
This can, of course, be avoided by using elastomer pipes. In this case, however, the rubber pipes themselves are the weak point, since they are substantially permeable to hydrocarbons. While fluoroelastomers have better barrier properties, they are extremely expensive. Connecting the PE nipples by means of rubber tubing onto a non-creeping connector, for example made from glass-fiber-reinforced nylon, is also complex in production and expensive. Furthermore, the tubing is still an undesirable source of emissions.
Direct connection, for example between a PE nipple and a nylon pipe fitted over it, likewise fails after a short period of time since the prestressing of the pipe causes the PE to creep, so that, on the one hand, the connection begins to leak, and, on the other hand, the joint strength under axial loading becomes unacceptably low.
Elevated temperatures in the region of the connection and the swelling caused by the fuel components make the creation of a low-permeability connection still more difficult.
Construction of a low-creep nipple is unsuccessful. First, because no suitable reinforced varieties of PE, adequate for the mechanical demands on the connection, are available and, second, the strength of a welded joint between a fiber-filled polymer and an unfilled polymer is not sufficiently high.
German Patent 42 39 909 discloses a connection intended to solve these problems. A pipe-like connector of a material A having a tendency to creep is encapsulated on one side with a second material, B, having a low creep tendency. In the contact area between the two materials, this pipe-like structure has, therefore, a layered construction AB. This connection technique has, however, not proved successful in practical trials. In contact with fuel, the material A swells strongly. Since the swelling on one side is restricted by the material B, the material swells and creeps in the other directions so that, after some time, the load transmission and the tightness of the connection are no longer ensured. This phenomenon is further amplified under mechanical load and/or on drying out of this pipe-like connector. Even modifying one of the two materials in order to achieve adhesion between the materials leads to a deterioration in leak-tightness because the modified material (generally PE) swells still more strongly.
Accordingly, there remains a need for connectors which overcome these problems.